Rethermalization system

ABSTRACT

A rethermalization system for storage of prepared meals in a refrigerated state, rethermalization of the meals in accordance with a rethermalization program, and maintenance of the rethermalized meal at a desired serving temperature is disclosed. Refrigerated meals are placed within racks in a rethermalization cart that is retained in a refrigerated area. Beneath the trays are located heater shelves containing one or more heating elements to heat selected food items located on the tray. The carts incorporate controllers which, upon receiving a start signal, provide power to the heater shelves of the cart in accordance with a rethermalization program. The controllers are specially adapted to enable a user to provide various heater shelves on the same cart with different programs to compensate for temperature stratification and warm and cool areas within the refrigerated environment. In an embodiment, the rethermalization program is a three stage rethermalization cycle with the food first heated to a temperature greater than the desired cooking temperature, the food is then maintained at the desired cooking temperature for a period of time and finally, the temperature is reduced and maintained at a desired serving temperature until the tray is removed from the cart or the system is turned off.

FIELD OF THE INVENTION

This invention relates to the field of refrigerated storage andrethermalization of food and particularly to an integrated storage andrethermalization system for providing an easy, efficient and reliablemeans for serving a large number of meals at a desired time.

BACKGROUND OF THE INVENTION

The preparation and serving of large numbers of meals in aninstitutional setting has long posed a variety of problems. The abilityto serve palatable meals with the various dishes being served at optimumtemperature often conflicts with efforts to make service of the mealseasier, more efficient and less manpower intensive.

The preparation, storage, rethermalization and service of a large numberof meals has evolved through several stages. Initially, trays would befilled with foods from various hot or cold storage containers areas justprior to serving and transported to the individual serving areas (suchas patient's rooms in a hospital). However, as facilities grew larger,the assembly of trays from a centralized area became very difficult ifnot impossible. Frequently in such a system, the time between trayassembly and service grew larger which resulted in food being served atan unpalatable temperature or with spoilage occurring.

Early attempts to overcome such problems resulted in the development ofstorage carts having separate hot and cold storage compartments. Theseseparate compartments would either be heated or cooled or would be wellinsulated in order to maintain the food at a desired temperature. Inuse, food would be loaded into separate hot and cold storagecompartments in a central food preparation area. The carts could then betransferred to various assembly locations. The individual meals couldthen be assembled on trays as desired and served. However, while suchdelivery systems did improve the time lag between assembly of the traysand service of the meal, they still required significant man power atserving time because these trays had to be assembled. As a result,frequently the hot food would be maintained hot for an extended periodof time and become unpalatable or, if all trays were assembled at once,some food would be cold by the time it was served. Additionally, mealservice would be spread out over the time required to assemble thetrays.

Another development was a food service system of trays and cartsincorporating heating elements which are provided in a refrigeratedenvironment. In this type of system, trays could be pre-assembledwhenever desired and loaded into the carts. In the refrigeratedenvironment food would remain cold. At a desired time, the heatingelements would be activated to rethermalize the food and to maintain thewarm food in a warm condition while not effecting the food which is toremain chilled. After the food had reached a serving temperature thecarts could then be rolled to the service locations and the traysserved.

However, even these systems have problems. For example, such devicestypically provide for a two stage rethermalization program which has atendency to either overcook the food or take an undesirable long time toreach the desired serving temperature. Typically, these two stagerethermalization cycles heat the food at a first, cooking, temperatureand if such temperature is selected to be high enough to rapidlyrethermalize the food, the food is often overcooked or scorched. If, onthe other hand, the initial heater temperature is low enough to avoidovercooking, the necessary rethermalization cycle is frequently toolong.

Additionally, such systems are not capable of adjusting for temperaturevariations within the refrigerated environment. Stratification of airwithin the refrigerator will occur because of the tendency of relativelywarmer air to rise. This tendency toward stratification is exacerbatedby the tendency of warmer air heated by the heaters to rise to the topof the refrigerated compartment. There will also be temperaturevariations throughout the refrigerator due to the location of registersfor the entry of chilled air into the refrigerated compartment. Thus,food at the top of the carts will tend to heat quicker than food nearthe bottom as the warmer air tends to accumulate at the top of therefrigerator. Also, carts located near the chilled air registers willtend to reach the desired rethermalization temperatures more slowly thancarts located in a relatively warmer area of the refrigerator. If notcompensated for, the temperature stratification and variation may resultin either the overheating of food or the under heating of food dependingon the location of the tray in relation to the temperature variations.

Furthermore, such systems have generally had a central controller which,if it malfunctioned, could result in an entire meal not being ready atthe desired time. Additionally, the use of a centralized control systemhas made it very difficult, if not impossible, for these control systemsto compensate for the temperature stratification and variation withinthe refrigerator. Also, such systems rarely provide significant userfeedback relating to whether the carts are properly connected in therefrigerator and the overall functioning of the system.

SUMMARY OF THE INVENTION

The above discussed problems, and others problems, are overcome in arethermalization control system made in accordance with a preferredembodiment of the present invention. In a preferred embodiment, there isprovided a rethermalization system for rethermalizing refrigeratedfoods, for maintaining the foods in a refrigerated state until they arerethermalized, and heating certain foods to a desired temperature at aserving time while maintaining certain other foods in a chilledcondition. In this embodiment, the rethermalization system comprises aplurality of trays for supporting food items thereon which include thefood items to be rethermalized. A rethermalization cart is provided forholding the trays upon which the food is to be served. A plurality ofheater shelves, including individual heating elements, are disposed inthe cart under the trays for selectively rethermalizing the desiredfoods located on the trays. After being loaded with trays, therethermalization cart is placed in a refrigerator adapted to receive thecart which maintains food at a desired refrigerated temperature; thecart is preferably placed at a docking location within the refrigerator.A power supply and controller is provided for supplying power to atleast one of the heaters according to a rethermalization program whichprovides that the heater is maintained within a first temperature rangefor first time interval, a second temperature range for a second timeinterval, for cooking the food items at a desired temperature, and athird temperature range for a third time interval, for maintaining thefood item at the desired serving temperature. In one embodiment of theinvention, the first temperature range is selected to be hotter than thedesired cooking temperature of the food item and the second temperaturerange is selected to be hotter than the desired serving temperature. Ina further embodiment of the invention, the power supply and controllercompensates for temperature stratification and variation within therefrigerator by controlling power so that heaters in relatively coolerareas of the refrigerator achieve a higher temperature during at leastone of the predetermined time intervals than heaters in a relativelywarmer area of the refrigerator.

In another embodiment of the invention, the docking location furtherincorporates a cart detection means for sensing the presence or absenceof a rethermalization cart and generating a detect signal when a cart ispresent. The detect signal may then be provided to the power supply andcontrol means which is responsive to detect the signal and which willnot initiate a rethermalization program for that cart in the absence ofthe detect signal.

In an alternative embodiment of the present invention, in addition tothe plurality of trays, the rethermalization cart, the heater shelvesand the refrigerator, there is also a provided supply of power and firstand second controllers. The first controller functions to generate astart signal a predetermined time interval before the desired servingtime. The second controller is connected between the supply of power andthe heaters and is responsive to the start signal to supply and controlpower to the heaters in accordance with at least two rethermalizationprograms. The rethermalization programs are adapted to compensate fortemperature stratification within the refrigerator by controlling thetemperature of the heaters during a portion of the rethermalizationprogram so that heaters in relatively cooler areas of the refrigeratorachieve higher temperatures as compared to heaters in relatively warmerareas of the refrigerator.

In a preferred embodiment, the second controller may include a pluralityof individual heater controllers for controlling the supply of power tothe heaters in accordance with the rethermalization programs. In thissystem, each one of the heater controllers may operate under the controlof at least one rethermalization program where the rethermalizationprogram of at least one heater controller differs from otherrethermalization programs. The differences in the rethermalizationprograms are such that the different programs compensate for temperaturestratification and variation within the refrigerator by heating at leastone heater to a higher temperature relative to other heaters.

In a further embodiment of the present invention, the heater shelves maycontain at least two heating elements of different sizes and the secondcontroller may be adapted such that different rethermalization programsare followed for heaters of different sizes. Also, in one embodiment ofthe present invention, the first controller may include a programmabletimer for generating a plurality of start signals in accordance with apredetermined meal schedule so that each start signal initiates therethermalization of a different meal. In a further embodiment of thepresent invention, each of the heaters may have a temperature sensormeans associated therewith for sensing the temperature of the heater,generating a temperature signal corresponding to the temperature of theheater and providing the temperature signal to the second controller.

BRIEF DESCRIPTION OF THE DRAWINGS

These and further features of the invention will be best understood byreference to the following detailed description of a preferredembodiment when considered in conjunction with the Figures in which:

FIG. 1A is a view of the rethermalization system showing the primaryuser accessible features;

FIG. 1B is a view of a rethermalization cart for use in the presentsystem;

FIG. 2 is a simplified circuit diagram showing the control features ofthe present system;

FIG. 3 is a circuit diagram of the electronic components associated withthe refrigerator of the system;

FIG. 4 is a circuit diagram of the memory features of a firstcontroller;

FIG. 5 is a circuit diagram of the timing and display features of thefirst controller;

FIG. 6 is a circuit diagram of the user interface features of the firstcontroller;

FIG. 7 is a schematic of a preferred rethermalization cart;

FIGS. 8A, 8B and 8C are top, side and perspective views of a foodservice tray for use in the present system;

FIG. 9 is a schematic of the wiring harness for a rethermalization cartwith respect to power supply;

FIG. 10 is a circuit diagram of a 14 volt DC power supply for arethermalization cart;

FIG. 11 is a schematic of the wiring harness for a rethermalization cartfor one heater controller and two heater shelves;

FIG. 12 is a circuit diagram of the power supply and heating elementcontrol features of a heater controller;

FIG. 13 is a circuit diagram of the memory and timing features of aheater controller;

FIG. 14 is a circuit diagram of the program selection and temperaturesensing features of a heater controller;

FIG. 15 is a circuit diagram of the manual features of a heatercontroller; and

FIG. 16 is a graph representing a preferred rethermalization program.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

With reference now to FIGS. 1A and 1B there is shown a preferredembodiment of the rethermalization system of the present invention. Thepreferred rethermalization system utilizes a refrigerator 20 into whicha desired number of rethermalization carts 22 may be placed; in theembodiment represent by FIGS. 1A and IB a single cart 22 may be placedin the refrigerator 20. Preferably, the carts 22 are located at dockinglocations within the refrigerator 20. In an alternate embodiment, therefrigerator 20 may be of an institutional type and well known in theart modified to incorporate the features of the present invention andmay accommodate multiple rethermalization carts.

Preferably, the refrigerator 20 incorporates at least one dockinglocation 24 into which the cart 22 may be placed. The precise number ofdocking locations 24 is variable and will depend on the number of carts22 desired to be utilized. The docking location 24 preferably includesan outlet 26 for making an electrical connection with a docked cart 22which provides electrical power to the cart. Also, in the preferredembodiment, the docking location incorporates a cart detection device,such as a limit switch 28 in the back of the docking location, to detectwhether a cart is present or not. It should be noted that the cartdetection device need not necessarily be a limit switch in the back ofthe refrigerator, but could be made from a variety of various detectiondevices located at any number of places at the docking location.

In the preferred embodiments, the refrigerator may incorporate a varietyof different monitoring features in addition to the cart detector 28.For example, referring to FIG. 3, a switch 30 may be used to determineif the door of refrigerator is open. Additionally, a temperature sensingdevice 32 may be located within the refrigerator to generate atemperature signal.

In the preferred embodiment, a master controller 34 (FIG. 1A) isprovided on the refrigerator 20. This controller 34 is used to monitorthe various sensing devices, such as the cart detector 28, the door openswitch 30 and the temperature sensor 32 (FIG. 3) in the refrigerator andprovide appropriate user feedback on the refrigerator display 36 andLEDs 39 (FIG. 1A). For example, the master controller would monitor thesignals from these devices and would analyze the signals according toon-board instructions. These instructions could include provisions forsounding an alarm when the temperature signal from the temperaturesensor indicated that the temperature within the refrigerator exceeded apreset limit. Also, the master controller could sound an alarm when thedoor switch indicates that the door had remained open longer than apreset time. Finally, the signals from the cart detector 28 (FIG.1A)could be used to determine if carts were in place and the control systemcould provide a display to indicate that status to a user.

In addition to monitoring various aspects of the refrigerator 20, thecontroller 34 (FIG. 1A) is a part of the rethermalization process.Generally, the rethermalization system functions to keep food itemsstored within the refrigerator safely refrigerated until they are to beserved. The system operates to begin a rethermalization cycle apredetermined time interval before the desired serving time. The exactstart of the rethermalization cycle will depend upon the length of thecycle and the desired serving time.

The master controller 34 (FIG. 1A) serves to initiate therethermalization cycle. The master controller provides for user input,via push buttons 38 located on the control panel, to enable a user toselect the desired meal serving time. In the preferred embodiment, theuser may program multiple serving times corresponding to the servingtimes for various meals such as breakfast, lunch and dinner. After thesetimes have been programmed into the master controller 34, on-boardinstructions will determine when the rethermalization cycle should beinitiated. For example, if the programmed serving time is 8:00 a.m. andthe rethermalization cycle lasts 45 minutes, master controller 34 wouldprovide power to the carts 22 (FIG. 1B) at 7:15 a.m. to begin the cycle.Alternatively, the power supply to the carts 22 could be constant andsome type of logic signal provided to the carts 22 to initiaterethermalization.

Referring now to FIG. 2, there as shown is a simplified block circuitdiagram illustrating the control system of the present invention. Amaster controller 34 is located on the refrigerator 20 and includes adisplay 36, and keys 38 and LEDs 39. A user inputs instructions to thecontroller 34, through the keys 38 and information is displayed back tothe user through display 36 and LEDs 39. For example, a user may inputthree different start times, for breakfast, lunch and dinner, using thekeys 38, and the start times will be shown on display 36. The mastercontroller 34 provides output commands through lines 40 that are appliedto a plurality of second controllers represented in FIG. 2 bycontrollers 41a and 41b. In the preferred embodiment, ten controllerssuch as 41a are provided, but only two are shown in FIG. 2 for thepurpose of clarity.

Controller 41a issues control commands on lines 42a that are provided toa plurality of switches 43a, which are supplied power from a powersource 44 through lines 45. The switches 43a are electronic switchingdevices that control the amount of power flowing through them. Thus, theswitches 43a can turn the power off, apply full power, or apply apercentage of full power.

Power is supplied from the switches 43a through lines 46a which areconnected to heaters 47a mounted on a pair of heater shelves 48A. Asshown in FIG. 2, two thermistors 49a, are positioned beneath the heaters47a for detecting the temperature thereof. Likewise, four manualswitches 50a are mounted on the heater shelves 48a, and each of theswitches 50a are associated with one of the heaters 47a, so that theswitches 50a may be used to turn the heaters on and off. The thermistors49a and the switches 50a provide feedback control signals through lines51a, to the controller 41a.

In operation, when the master controller 34 provides a start signal online 40, controller 41a will begin a cooking program which is describedin more detail hereinafter. In accordance with the cooking program, thecontroller 41a issues control signals over lines 42a to turn theswitches 43a on to a desired degree. The switches 43a then apply powerto the heaters 47a, and the thermistors 49a sense the temperature of theheaters and provide signals corresponding to the temperature back to thecontroller 41a through the control lines 51a. When the heaters 47a reacha desired temperature, the controller 41a reduces the power to theheaters, or turns the power off, by controlling the switches 43a. Thus,the controller 41a individually controls the temperature of each heater47a and each heater may be controlled to a different temperature, ifdesired.

The switches 50a also provide control signals to the controller 41a andeach switch is associated with one heater. Thus, the user can manuallyactuate the switches 50a to turn one or more of the heaters 47a on oroff. When one of the switches 50a is switched off, a control signal issensed by the controller 41a and the controller 41a issues a command toan appropriate one of the switches 43a to turn the power off to theselected heater 47a which is associated with the switch 50a that wasturned off.

The controller 41b controls the heaters 47b in a manner identical tothat described above with respect to a controller 41a and heaters 47a.Controller 41b issues commands through lines 42b to the switches 43b andthey control power supplied through lines 46b to the heaters 47b onshelves 48b. Thermistors 49b provide temperature signals through lines51b back to the controller 41b and thereby provide the controller 41bwith the temperature of heaters 47b. Likewise, switches 50b providecontrol signals to the controller 41b and in response thereto, thecontroller 41b turns the heaters 47b on and off using switches 43b.

There are numerous advantages associated with using multiple controllerssuch as controllers 41a and 41b to control the heaters, such as 47a andb. First, each controller 41a and 41b includes ten position switches 52aand 52b. The controllers 41a and 41b are each programmed with tendifferent cooking programs which are manually selected using theswitches of 52a and 52b. For example, 52a may be manually set to program1 and 52b may be manually set to program 2. Thus, when a start signal isreceived from master controller 34, each of the controllers 41a and 41bwill begin a cooking program, but they will be different. For example,controller 41b, running program 2, may cause its heaters 47b to achievea higher temperature and hold that higher temperature for a longer timethan heaters 47a.

In the preferred embodiment, each controller 41a and 41b is providedwith the same set of ten programs. However, it will be appreciated thateach controller 41a could be provided with a different set of programs,such that program 1 in controller 41a was different from program 1 incontroller 41b.

The advantage of multiple controllers and multiple programs as describedabove is that each heater can be separately controlled to compensate forvariations in temperatures or cooking conditions within the refrigerator20. That is the variations in temperature within the refrigerator 20will cause some of the heaters 41a to be less effective or moreeffective than others in cooking food associated therewith. Thus, it isdesirable to vary the cooking program according to the environmentalconditions of each heater, such as heater 47a.

In general, it is preferred that each controller, such as 41a, controltwo heater shelves, such as 48a, and four heaters, such as 47a. It isfurther preferred that the controller 41a control all of the heaters 47ato follow the same cooking cycle. And that is, the controller 41a willattempt to cause all of the heaters 47a to follow the same cookingcycle. Preferably, each heater will be powered to achieve a firsttemperature for a first period of time, than the power will be changedcausing the heaters to achieve a second temperature for a second periodof time, and then the power will be changed again causing the heaters toachieve a third temperature for a third period of time. However, asmentioned above, the single controller 41a could control each of theheaters individually so that each is following a slightly differentcooking cycle. Although each controller 41a and 41b, in the preferredembodiment, has the same set of programs, and it is also preferred thateach controller 41a and 41b will have a different selected program usingthe manual switches 52a and 52b.

As mentioned above, FIG. 2 is a simplified diagram intended toillustrate the preferred control system, and certain details have beenomitted for purposes of clarity. In the discussion below, additionaldetails of the preferred embodiment are described.

Referring now to FIG. 3, a circuit schematic of the first control systemand its inputs may be described. Power from a 208 V AC three-line powersupply 54 is provided. 120 V/AC power is picked off from the 208 V inputby connection to one hot line 56 and neutral 58. This power is providedthrough master switch 60 to a 120 V-12 V step-down transformers 62 and64. 12 V/AC is supplied from transformer 62 to power a digitalthermometer 66 to provide users with an indication of the refrigeratortemperature. 12 V/AC from the other transformer 64 is provided throughpower conversion circuitry to a circuit board 68 containing the mastercontroller 34 (FIG. 2). Additionally, input from the temperature sensor32, door switch 30 and cart detector 28 are provided by lines 70, 72 and74, respectively to the circuit board 68. Power from the 208 V AC lineis also provided to a receptacle 26 located at the docking location 24(FIG. 1A).

The master controller 34 (FIG. 1A) on circuit board 68 also controls amercury switch 78 which further controls a three pole mercury switch 80which provides power to the receptacle 26.

Referring now to FIG. 4, the details of master controller 34 (FIG. 1A)may-be described. The primary feature of the master controller 34 is amicrocontroller 82. Preferably, the microcontroller 82 is an 8 bitmicrocontroller such as an 80C31. The schematic of FIG. 4 shows theassociated memory circuitry of microcontroller 82. Integrated circuit 84is a 16 bit PROM chip which contains the necessary software forproviding the control features of the master controller 34. Since themicrocontroller 82 is an 8 bit device and the PROM 84 is a 16 bitdevice, a latch 86 allows for the proper communication between themicrocontroller 82 and PROM 84. In operation, information from themicrocontroller 82 is provided in 8-bit words to the PROM 84. The first8 bit portion is provided to the latch 86 and the second 8-bit portionis provided directly to the PROM 84. In this manner, both 8 bit portionsmay be provided, from the latch 86 and microcontroller 82, as a 16-bitword to the PROM 84. The numbers from the electrical connectionsadjacent the integrated circuits represent the standard pin numbers fromthe various integrated circuits throughout the figures while thedesignations such as PO.O indicates the port number of themicrocontroller before the decimal and the bit number following thedecimal (for example, PO.O would indicate bit O of port O). Pin number29 from the microcontroller 82 provides the appropriate logic to thePROM 84 to control the read/write functions of the PROM 84.

Referring now to FIG. 5, the timing and display functions of the mastercontroller 34 (FIG. 1A) may be described. Integrated circuit clock 88 isa real time clock with on-board Random Access Memory (RAM) and batteryback up. Clock 88 provides the timing functions of the master controller34 as previously described with the user programmed serving times beingstored in the clock's on-board RAM. Pins 1, 2, 9-12 and 19 of themicrocontroller provide the necessary communication between themicrocontroller 82 and clock 88 while the remaining circuitry serves toisolate the clock RAM from power fluctuations due to the powering up anddown of the microcontroller 82.

Pin 3 from the microcontroller 82 represents the display output from themicrocontroller 82 to the display driver 90. The display driver 90drives the various displays associated with the master controller 34 andlocated on the control panel 36 (FIG. 1A). The display driver 90operates four discrete LEDs 92, 94, 96 and 98, and four digit displays100, 102, 104 and 106, according to the signal from the microcontroller82. Various clocks having on-board RAM, display drivers, discreet LED'sand digit displays are readily available for use in the presentinvention and may be substituted freely by those skilled in the art.

The remaining features of the master controller 34 may be seen withreference to FIG. 6 At the top of FIG. 6 is shown the power conversioncircuitry 108 necessary to convert the 12 V AC current from thetransformer 64 of FIG. 3 to the necessary 5 V DC signal used to powerthe microcontroller 82 and other integrated circuits and componentsassociated with the master controller 34 in ways well known in the art.

Pin 5, from the microcontroller 82 represents an output from themicrocontroller 82 corresponding to a high temperature condition in therefrigerator 20 and is used to trigger an audible alarm, buzzer 110, andmay be further output to a remote alarm device which is located somedistance from the control panel 36 of FIG. 1A. Pins 6 and 7 representadditional alarm outputs which could be used to drive remote indicatorsto indicate a high temperature condition or other situations about whicha user should be notified.

Other inputs to the microcontroller 82 are shown as they would be inputfor the controller 82 from the circuitry described with respect to FIG.3; the signals generated by the cart detector 28 on line 74 at pin 33,door switch 30 on line 72 at pin 34 and temperature sensor 32 on line 70at pin 35 as were previously described with respect to FIG. 3. Finally,pins 36-39 represent inputs which correspond to inputs from the fourpush buttons 112, 114, 116 and 118 located on the control console 36(FIG. 1A). These push buttons 112-118 are used to program the mastercontroller 34 as was previously described. Furthermore, every time apush button 112-118 is depressed, a signal is generated by themicrocontroller 82 at pin 8 which sounds the buzzer 110, this featureserves to provide the user with feedback to know that the input from thepush button has been detected.

Referring now to FIGS. 1B and 7 the design of a preferredrethermalization cart 22 may be described. Generally, therethermalization cart 22 is made of aluminum or any other lightweightconstruction material. The cart rests on wheels or casters 118 tofacilitate the movement of the cart. Tray supports 120 are provided toproperly position and hold a number of food service trays 122.Positioned below each tray support 120 is a heater shelf 124 whichcontains the heaters 126 used to rethermalize the food items on a tray122. Also located on each cart is a number of heater controller boards,a power supply and heater controllers which will be described more fullyherein.

Referring now to FIGS. 8a, 8b and 8c, the construction and use of apreferred food tray may be described. In use, the trays 122 are loadedwith prepared meals with the food items to the rethermalized locatedwithin containers 128. These containers are placed in special holders130 and 132 on the tray 122 which allow the bottom of the containers 128to extend beyond the bottom of the tray 122. The trays are then coveredto minimize drying out of the food and thermal convection with covers134. These trays 122 are then placed within the cart 22 on the traysupports 120 (FIG. 7). The containers 128 are designed so that theycontact the heater shelf 124 (FIG. 7) when the tray 122 is properlyloaded. Thus, when the heaters are turned on, the food within thecontainers 128 contacting the heater shelf 124 will be rethermalized.

Once a cart 22 has been loaded, it is then placed in the dockinglocation 24 of FIG. 1A and plugged into the outlet 26 associatedtherewith. The second controllers (41a and b of FIG. 2) located on thecarts await the start signal from the master controller 34 or a powersignal as was previously described. Once the start signal is received,the heaters controllers provide power to the heaters associatedtherewith in accordance with a rethermalization cycle stored on theheater controller. Once the rethermalization cycle is complete, thecarts 22 may then be removed from the refrigerator 20 and transported toa location where meals are to be served. It should be noted that onlythe food located in containers 128 which contact the heater shelves 124will be heated, food located on other portions of the tray will remainchilled.

With reference now to FIG. 9, the power supply and distribution system136 located on each cart 22 (FIG. 7) may be described. 208 V/AC powerfrom the main line is provided to the cart through plug 138 which mateswith outlet 26 as was previously described. As is known in the art, the208 V AC input is provided by two "hot" lines 140 and 142, a neutralinput 144 and ground 146. Each hot line and neutral line is provided toterminals 148, 150 and 152 from which lines to the various heatershelves may be connected. As is known in the art, a 120 V AC powersignal may be obtained by connecting across one hot line and neutral ofthe 208 V input. The wiring harness shown in FIG. 9 is particularlydesigned for a rethermalization cart designed to accommodate twentytrays and forty heaters and the number of electrical lines wouldnecessarily vary according to the number of tray locations on the cart.

Power is provided to a converter 154 from one hot line terminal 152 andthe neutral terminal 150. With reference to FIGS. 9 and 10 the design ofthe converter 154 may be described. 120 V AC power is provided to theconverter as previously described. The 120 V AC signal is transmittedfrom lines 156 and 158 through a step-down transformer 160. Power at theoutput side of the transformer 160 is rectified by a bridge 162 toprovide a 14 V DC power signal at lines 164 and 166. In addition, a zerocrossing detector 130 detects zero crossings of the AC signal andgenerates a zero crossing signal on line 168.

Referring now to FIG. 11 the connections between a single heater controlboard 170 and two heater shelves 172 and 174 are shown (this wouldcorrespond to controller 41a and associated circuitry as described withrespect to FIG. 2). Lines 176 and 178 are inputs from the hot terminals148 and 152 (FIG. 9) from the power supply. Lines 180 and 182 are powerlines from the board 170 to the large heater 192 and small heater 194located on one heater shelf 174. Lines 188 and 190 are power lines fromthe board 170 to the heaters 184 and 186 located on the other heatershelf 172. Additionally, line 196 represents a neutral line from theneutral terminal 150 (FIG. 9) which is provided to amp connectors 198and 200 and to the heaters 184, 186, 192 and 194. Lines 202, 204, 206,208 and 210 carry signals from electronic switches 212, 214, 216 and 218which may be used to manually disable individual heater shelves. Theseelectronic switches preferably generate logic signals corresponding tothe position of the switch.

Thermistor inputs 220, 222, 224 and 226 are provided to the controlboard 170 from thermistors 228, 230, 232, 234, which are located at eachheater. The thermistors provide temperature information for use in therethermalization cycle.

14 V DC power for the control components on the heater board 170 isprovided from the converter previously described by lines 164 and 166and the zero crossing signal is provided on line 168.

Referring now to FIGS. 12 through 15, the heater control circuit may bedescribed in detail. With respect to FIG. 12, the power controlfunctions of the heater circuitry may be described. Initially, asindicated at the left of the drawings in FIGS. 12 through 15, theindication 236 represents a microcontroller located on the circuit board170 (FIG. 11). The preferred microcontroller 236 for use in the heatercontrol circuitry is an 8 bit, 68HC11 microcontroller which may be madeby a variety of companies. With reference to FIG. 12, the circuitry 238shown at the top of the sheet pertains primarily to providing power tothe microcontroller 236 and the associated integrated circuits whichrequire power to operate, from the power supply 154 located on therethermalization cart 22 as shown in FIG. 9. The power from lines 164and 166 provide 14 V DC rails which are processed through a voltageregulator 244 to provide 5 V DC power for the microcontroller 236. Aswas the case with respect to FIG'S. 4-6 the standard pin numbers areshown with respect to the various integrated circuits. The input powerfor the microcontroller 236 is input to the microcontroller at pins 48and 23 as indicated in the drawing. Additionally, the zero crossingsignal previously described with respect to the power supply located onthe cart 22 is provided through line 168 to pin 41 of themicrocontroller 236 which is the IRQ input for the microcontroller 236.As indicated at pin 40 of the microcontroller 236, the XIRQ input istied high through a resistor.

Pins 2, 3, 4 and 5 of the microcontroller provide the control logic outto the heater controller circuitry. The indication such as PA6 at pin 2indicate the output port and bit number from the microcontroller throughwhich the logic is supplied. Integrated circuits 246, 248, 250 and 252are optical couplers which serve to isolate the microcontroller 236 fromthe high voltages associated with the heaters and the power supplycircuitry for the heaters. These optical couplers 246, 248, 250 and 252are made by a variety of companies and function to convert the heatercontrol logic signals from the microcontroller 236 into an opticalsignal which is transmitted to another portion of the optical couplersand reconverted back to an electronic signal. In this manner there is nodirect electrical contact between the microcontroller 236 and the highvoltage power supply circuitry associated with the heaters.

The control logic is provided to triacs 254, 256, 258 and 260 whichcontrol the supply of power to the heaters, and the power in from the208 Volt AC rails by lines 176 and 178 of FIG. 12, is supplied to thetriacs. Power out to one heater (such as heater 184 of FIG. 11) iscontrolled by triac 254 and is output through line 190 to the heater. Aswas previously described with respect to the rethermalization cart, oneline from the 208 Volt AC three line input would be provided at 178while a neutral line would be provided to each of the heaters. Withrespect to the second heater (such as heater 186 of FIG. 11), triac 256would supply power from the same 120 V rail previously described withrespect to triac 254 to the second heater through line 188 according tothe logic provided by the microcontroller 236. Movistors 262, 264, 266and 268 serve to suppress transient voltages caused by variations inpower to the heaters.

With respect to the lower half of FIG. 12, the optical couplers 250 and252, triacs 258 and 260, movistors 266 and 268, power in line 176 andthe power out lines 182 and 180 would serve to control two heaters (suchas heaters 192 and 194 of FIG. 11) as was previously described. It wouldbe possible to vary the control circuitry to control different numbersof heaters and heater shelves without departing from the scope of theinvention.

The circuit 270 at the bottom of FIG. 12 is associated with the resetinput at pin 39 of the microcontroller 236. The reset pin is tied highthrough a capacitor and resistor so that no reset signal will be givenwhen power is supplied to the board. The only occurrence of a low signalat the reset at pin 39 of the microcontroller 236 would occur when poweris turned off. This adaptation is preferred where power to the cart 22is provided by the master controller 34. In that embodiment therethermalization cycle would begin when power is supplied to the cart22. In an alternate embodiment where power is constantly available tothe cart 22, the reset circuitry 270 would need to be modified to acceptlogic signals from the master controller 34.

Referring now to FIG. 13, the memory and timing functions of themicrocontroller 236 may be described in detail. The circuitry 272 at thetop of FIG. 13 represents control circuitry for control of the read andwrite functions of the microcontroller 236 and its associated memory.For example pins 27 and 28 of the microcontroller correspond to theenable and read/write logic output of the microcontroller 236 and areprovided as input to a NAND gate 274. The output of the NAND gate 274 isprovided to the output enable input at pin 22 of an erasableprogrammable read only memory (eprom) chip PROM 276, preferably a27C256. Additionally, the output at pin 9 of the microcontroller 236,which corresponds to the high order address of the microcontroller isprovided as both inputs to second NAND gate 276. The output of this NANDgate 276 is provided to the chip enable input at pin 20 of the PROM 276.Pins 31-38 of the microcontroller 236 represent the low order addressoutput of the microcontroller 236. Similarly, pins 10-16 of themicrocontroller 236 represent the high order address output of themicrocontroller 236.

In use, since the microcontroller 236 is an 8 bit device and the PROM276 is a 16 bit device, some type of circuitry is needed to allow thesediffering devices to communicate. Information from the low order addressof the microcontroller 236 would be input into a latch 280, preferably a74HC573, for subsequent input into the PROM 276. After the low orderaddress has been inputed into the latch 280, the high order address maybe directly input into the PROM 276. In this manner, a 16 bit word maybe directly read into the PROM 276 simultaneously, although themicrocontroller 236 is only able to output 8 bits at a time.

The circuitry 282 at the bottom of FIG. 13 supports a crystal 284 whichprovides an operating frequency to the on-board clock located on themicrocontroller 236. The crystal 284 provides an 8 Mhz signal at pins 29and 30 of the microcontroller 236 which is used by an on-board clock tokeep time in order to coordinate its various functions.

Referring now to FIG. 14, circuitry relating to the selection ofrethermalization programs and temperature sensing functions of thecontrol system may be described. The various rethermalization programsare preferably stored in the PROM 276 of FIG. 13 which was previouslydescribed. In the preferred embodiment, multiple rethermalizationprograms may be stored on the PROM 276 and then selected by a user ofthe device or a service technician. The various rethermalizationprograms are preferably selected by proper positioning of a rotarybinary coded decimal switch 286. As shown in FIG. 14 the binary codeddecimal switch 286 is provided as input at pins 1, 47, 43 and 42 of themicrocontroller. Depending on the position of the switch 286, a binarycoded decimal number between zero and nine will be provided to themicrocontroller 236 which will select a correspondingly numberedrethermalization program. It should be noted that a multitude of variousdevices other than a rotary binary coded decimal switch may be used toselect the rethermalization programs and such substitution may be madewithout affecting the scope of the invention.

Pins 17-20 of the microcontroller represents inputs from thermistorslocated at their associated heaters, as was previously described withreference to FIG. 11. The temperature information is necessary since therethermalization programs are temperature dependant as will be morefully described below. The thermistors serve to provide an electronicsignal corresponding to the temperature sensed underneath each heatingelement. The analog temperature signals from the four thermistors areprovided as inputs at junctions 288, 290, 292 and 294 and further inputto the microcontroller 236. Reference voltage signals are provided bycircuitry 296 to generate a high voltage reference and low voltagereference at pins 22 and 21 of the microcontroller 236. These signalsallow an on-board analog to digital converter on the microcontroller 236to convert the analog thermistor signals to digital signals.

Referring now FIG. 15, the remaining features of the second controlsystem may be described. Junctions 298, 300, 302, 304, 306, 308 and 310represent inputs from the electronic switches located at the heatershelves previously described with respect to FIG. 11. The input atjunction 300 would represent the common input which completes thecircuit with all of the switches. The input at junction 298 wouldcorrespond to the input from a master switch on a particular shelf whichwould serve to disable or enable both heaters located on a given shelf.The input at junctions 302 and 304 would correspond to switches used tomanually enable or disable the individual heaters of a given shelf. Theinputs at junctions 306, 308 and 310 would represent the inputs fromswitches corresponding to the second heater shelf controlled by thesecond control system 170 (FIG. 11). For example, the input at junction304 could correspond to the shelf switch which enables or disables theentire heater shelf, while the inputs at junctions 306 and 308 wouldrepresent the switches for the individual heaters located on that shelf.In the preferred embodiment, the shelf switches which would be input atjunctions 298 and 304 are not included and thus, these inputs could betied to a common line as indicated in FIG. 11.

With an understanding of the basic features of the invention, thegeneral functioning of the overall rethermalization system may bedescribed. In use, the various rethermalization carts would be loadedwith refrigerated or frozen prepared meals by placement of trays withinthe cart. In one embodiment, the carts would then be taken to locationsclose to their various serving locations and placed in refrigeratorsdesigned to hold a single cart. Alternatively, the carts could becollected at various centralized areas where larger refrigeratorsadapted to hold several carts may be utilized. The carts are then placedwithin docking locations within the various refrigerators and anoperator programs the refrigerator through push buttons located on therefrigerator control console. By programming the refrigerator controlconsole, the desired meal serving time may be input into the firstcontrol system which would then calculate the appropriate starting timefor the rethermalization cycle.

As was previously described, there are a plurality of second controllerslocated on the various rethermalization carts with each secondcontroller preferably controlling two heater shelves with each heatershelf containing two heating elements. At a predetermined start timedetermined by the first controller, the first controller supplies powerto the carts and further to the power supply located on the carts. Thispower is then further provided to the plurality of second controllerswhich initiates the selected rethermalization program located on each ofthe second controllers.

Referring now to FIG. 16, a graph of temperature versus time shows apreferred rethermalization control program. In the preferred program,the triacs located at the second controllers provide full power to theindividual heating elements until a temperature of 350° F. is attained;by monitoring the various thermistors, the second controller candetermine when each heating element has attained the desiredtemperature. The second controller varies the power supplied to thevarious heating elements through the triacs to maintain the desiredtemperature plus or minus 3° for a time interval of 16 minutes. Duringthe second phase of the rethermalization cycle, power is reduced so thatthe temperature of the heating element is allowed to drop to about 270°F. Then the controller functions to maintain the 270° F. temperatureplus or minus 3° until 36 minutes into the rethermalization cycle. Inthe final stage of the preferred rethermalization cycle, power is onceagain reduced to maintain a warming temperature of 210° F. plus or minus5°. The second controller will function to maintain this holdtemperature until the rethermalization cart is removed from therefrigerator or the rethermalization program is canceled. Additionally,at the end of the rethermalization cycle the first controller signals analarm in order to indicate that the cycle has been completed and thefood is ready to serve. In the preferred embodiment, the firstcontroller is capable of storing multiple serving times so that a fullday's serving times may be programmed at one time. Thus, all that wouldremain to be done to prepare from one meal to the next would be toremove the meal that is ready and place a new reloaded cart into therefrigerator at the docking location.

As was described previously, a variety of rethermalization programs maybe stored on the second controllers and selected with a rotary binarycoded decimal switch providing programs coded from zero to nine. Thecommon feature of all of the rethermalization programs is that the foodundergoes a three stage rethermalization cycle wherein the food isinitially heated to a temperature above a desired cooking temperaturefor a time interval, then the food is maintained at a desired cookingtemperature for a second time interval and finally the food ismaintained at a desired serving temperature until the cart is removedfrom the refrigerator. The use of plurality of controllers allows forselecting different rethermalization programs for each controller whichallows for a user to compensate for various effects.

For example, as warm air has a tendency to rise, the regions near thetop of the refrigerator will be warmer than the region near the bottomof the refrigerator. Thus, food at the bottom of the refrigerator maynot be warmed or cooked if the same rethermalization program is used forthe heaters located at the bottom of the refrigerator and the heaters atthe top of the refrigerator. The binary coded decimal switch settingcould be selected to choose a different rethermalization program forheaters located in relatively warmer or cooler regions of therefrigerator. In this manner, heaters located in relatively coolerportions of the refrigerator could maintain a higher temperature for atleast a portion of the rethermalization program or could be maintainedat a high temperature for a longer period of time for at least a portionof the rethermalization program than heaters located in relativelywarmer areas of the refrigerator.

Additionally, where many rethermalization carts are placed in a largerefrigerator, the temperature of the refrigerator may vary from locationto location within it. Such variations can occur due to exhaust andinlet air ducts and convection effects. Thus, carts placed in variousareas of the refrigerator may have their rethermalization programsadjusted by selecting different programs in order to compensate forregions of differing temperature within the refrigerator.

The foregoing description of a preferred embodiment is for the purposesof illustration and not limitation. For example, while in the preferredembodiment a single second controller controls two heater shelves, thecontroller could be adapted by one skilled in the art to control anynumber of heater shelves. Also, while the construction was described asan individual heater shelf containing two heating elements, any numberof desired heating elements could be placed on a heater shelf or theheating elements could be individual heating elements not containedwithin a heater shelf. Also, while the preferred embodiment utilizes afirst and second control systems, these control systems could becombined and located on the individual refrigerators or on therethermalization carts themselves without departing from the scope ofthe invention. Finally, while particular electronic components weredescribed in the specification, it is well known in the art thatsubstitutions of components may be freely made to achieve the samepurpose.

I claim:
 1. A rethermalization system for rapidly rethermalizingrefrigerated foods, for maintaining the foods in refrigerated stateuntil they are rethermalized, and heating certain foods to a desiredtemperature at a serving time while maintaining certain other foods in achilled condition comprising:a plurality of trays for supporting fooditems thereon including food items to be rethermalized; arethermalization cart for holding a plurality of trays; a plurality ofheater shelves, including heaters, disposed in the cart under the traysfor selectively rethermalizing desired foods located on the trays; arefrigerator adapted to receive said rethermalization cart formaintaining the food at a desired refrigerated temperature andcontaining a docking location; and control means and power supply forsupplying power to at least one heater according to a rethermalizationprogram such that said heater is maintained within a first temperaturerange for a first time interval, a second temperature range for a secondtime interval for cooking said food items at a desired temperature and athird temperature range for a third time interval for maintaining saidfood item at a desired serving temperature, wherein said firsttemperature range is higher than the second cooking temperature range ofthe food item to be rethermalized.
 2. The rethermalization system ofclaim 1 wherein during said second time interval said second temperaturerange is hotter than the desired serving temperature.
 3. Therethermalization system of claim 1 wherein said power supply and controlmeans comprises:a supply of power; first control means for generating astart signal; and second control means connected between said supply ofpower and said heaters and being responsive to said start signal forsupplying and controlling power to said heaters in accordance with saidrethermalization program.
 4. The rethermalization system of claim 1wherein said power supply and control means compensates for temperaturestratification within said refrigerator by controlling the power to saidheaters so that heaters in relatively cooler areas of the refrigeratorachieve a higher temperature during at least one of said predeterminedtime intervals than heaters in relatively warmer areas of therefrigerator.
 5. The rethermalization system of claim 1 furthercomprising cart detection means located at said docking location withinsaid refrigerator for sensing the presence or absence of arethermalization cart and generating a detect signal when a cart ispresent, wherein said detect signal is provided to said power supply andcontrol means and said power supply and control means is responsive tosaid detect signal such that said rethermalization program will not beinitiated in the absence of said detect signal.
 6. The rethermalizationsystem of claim 1 further comprising outlet means within saidrefrigerator located at said docking location for providing power andsignals to the rethermalization cart located in said docking location.7. The rethermalization system of claim 1 further comprising saidcontrol means located in part on said rethermalization cart, saidcontrol means containing said rethermalization program.
 8. Therethermalization system of claim 3 wherein said second control means islocated on said rethermalization cart.
 9. A rethermalization system forrapidly rethermalizing refrigerated foods, for maintaining the foods ina refrigerated state until they are rethermalized, and heating certainfoods to a desired temperature at a serving time while maintainingcertain other foods in a chilled condition comprising:a refrigerator formaintaining the food at a desired refrigerated temperature andcontaining a docking location; a rethermalization cart adapted to bereceived within said docking location of said refrigerator; a pluralityof support means disposed within said rethermalization cart forsupporting food items, said support means further comprising heatershelves, including heaters; a plurality of food service trays adapted toreceive a plurality of food items thereon, including food items to berethermalized, said food service trays further adapted to be supportedwithin said rethermalization cart by said support means and positionfood items to be rethermalized over said heaters in conductive heatexchange relationship with said heater shelves of said support means;and control means and power supply for supplying power to at least oneheater according to a rethermalization program, said rethermalizationprogram defining at least two temperature ranges at which said heatersare maintained, the first of said two temperature ranges beingmaintained for a first time interval and the second of said temperatureranges being maintained for a second time interval, said secondtemperature range corresponding to a desired cooking temperature andsaid first temperature range being greater than said second temperaturerange.
 10. The rethermalization system of claim 9 wherein said powersupply and control means comprises:a supply of power; first controlmeans for generating a start signal; and second control means connectedbetween said supply of power, said first control means and said heatersand being responsive to said start signal for supplying and controllingpower to said heaters in accordance with said rethermalization program.11. The rethermalization system of claim 9 further comprising cartdetection means located at said docking location within saidrefrigerator for sensing the presence or absence of a rethermalizationcart and generating a detect signal when a cart is present, wherein saiddetect signal is provided to said power supply and control means andsaid power supply and control means is responsive to said detect signalsuch that said rethermalization program will not be initiated in theabsence of said detect signal.
 12. The rethermalization system of claim9 wherein said food service trays further comprise segregated foodstorage areas, said food storage areas defining hot and cold foodstorage areas, said hot food storage areas corresponding to locations onsaid food service trays which coincide with said heaters of said heatershelves.
 13. The rethermalization system of claim 9 further comprisingsaid control means located in part on said rethermalization cart, saidcontrol means containing said rethermalization program.
 14. Therethermalization system of claim 10 wherein said second control means islocated on said rethermalization cart.